Abstract: An upper board fixed to a lower part of a structure; a lower board fixed to a foundation at the same position in a plan view with respect to the upper board; and four seismic isolation plates fixed to the upper and lower boards and extending in a cross direction in a plan view. The seismic isolation plates are U-shaped members obtained by bending a long steel sheet, and include an upper fixing part parallel to a lower fixing part, an upper inclined part and a lower inclined part that are closer to each other while separated from the upper and lower fixing parts, and a connecting part that connects the upper and lower inclined parts. The four seismic isolation plates are fixed to upper board at position where upper fixing parts do not overlap and are fixed to lower board at position where lower fixing parts do not overlap.